Generally, an airbag apparatus is mounted on a vehicle. The airbag apparatus is generally configured so that an airbag accommodated within, for example, a center portion of a steering wheel, a dash panel provided in the vicinity of a passenger seat and the like is instantaneously inflated in a case where a shock, which is generated at the vehicle when the vehicle collides, is detected by a collision detecting means such as an acceleration sensor and the like in order to protect an occupant seated on a seat having the airbag.
Generally, in the case where the airbag apparatus is mounted on the vehicle, a load sensing device for sensing (detecting) the occupant is provided at the seat having the airbag (e.g. JP2003-344145A, JP2002-286536A and JP2003-240627A). The known load sensing device includes a load detecting means for outputting a load signal in response to a strain generated at the known load sensing device, so that a load applied on the seat is detected on the basis of the load signal outputted from the load detecting means.
According to the known load sensing device, a significant zero-point displacement (a zero-point shift) may occur at the load signal outputted from the load detecting means because of the shock generated at the vehicle when the vehicle collides. In other words, the load signal outputted from the load detecting means may indicate a predetermined load even if the occupant is not seated on the seat and a load applied to the seat is substantially zero. Therefore, in this case, if the load sensing device is kept being used, the load sensing device may mistakenly determine that the occupant is seated on the seat. Accordingly, in this case, when the shock is detected by the collision detecting means, a warning indicator and the like may be actuated in order to notify the passenger of an occurrence of an abnormality and in order to urge a user of the vehicle to take the vehicle to a maintenance factory such as a car dealership and the like.
In a case where the vehicle is took to the maintenance factory and the like, a maintenance engineer needs to reset a zero-point in response to the abnormality warning (i.e. the zero-point displacement is solved). Then, the maintenance engineer executes a sensitivity test. Hereinafter, a set of the reset of the zero-point displacement and the sensitivity test is referred to as a zero-point adjustment. In a case where the maintenance engineer determines that the load sensing device is continuously usable, the load sensing device is allowed to be continuously used.
However, for example, in a case where the occupant hits or kicks the seat, the shock corresponding to the shock to be generated when the vehicle collides may be detected by the collision detecting means. Generally, chances of the significant zero-point displacement to occur at the load signal outputted from the load detecting means is very small, because the load applied to the seat in this case is about a level of power generated by a human being, and no significant zero-point displacement is likely to occur. However, in the case where the abnormality is alarmed to the user of the vehicle in the case where the shock generated by hitting or kicking the seat is detected as the load having the level indicating a collision of the vehicle and the user takes the vehicle to the maintenance factory and the like, the maintenance engineer needs to perform an unnecessary zero-point adjustment, which may result in increasing hours relating to the maintenance.
A need thus exists to provide a load sensing device which is not susceptible to the drawback mentioned above.